Pearsonites

Original Description: Test low trochospiral, weakly biconvex to planoconvex, with 6–10 chambers in the last whorl. Spiral side with subglobular to subquadrate chambers that increase very gradually in size; sutures slightly depressed to flush and slightly recurved to oblique. Umbilical side with triangular chambers; sutures nearly straight, depressed. Umbilicus generally widely bordered by coalescing circumumbilical muricae. Aperture a low arch extending toward the peripheral margin that is subrounded to subangular.Extra details from original publication: Etymology. Named in honor of Professor Paul N. Pearson for his outstanding contributions to the study of Paleogene foraminifera.

Wall texture. Nonspinose with thin muricae.

Species included. Three species (P. lodoensis, P. broedermanni, and P. anapetes) are now assigned to Pearsonites, based on both wall texture and morphological similarities.

Pearsonites lodoensis (Mallory, 1959), first described from the lowermost Eocene of the Lodo Formation (California), is characterized by having a rather large umbilicus, 6–7 chambers in the final whorl, a lobulate equatorial outline, and round-subangular peripheral margin. On the spiral side, it displays slightly depressed sutures that are very slightly recurved on the last chambers.

Pearsonites broedermanni (Cushman & Bermudez, 1949), described from lower Eocene strata of the Capdevila Formation (Cuba), has a weakly biconvex test that tends toward being planoconvex, a narrow umbilicus, a rounded periphery, and 6–7 chambers in the last whorl. The sutures on the spiral side are weakly depressed, and obliquely curved in the last whorl.

Pearsonites anapetes, described by Blow (1979) from the early middle Eocene (Zone P115 E9) at Kilwa (Tanzania), is characterized by a planoconvex test with 8–9 (rarely 10) almost equidimensional chambers, nearly straight oblique sutures that are barely depressed in the last chambers, and a relatively broad umbilicus.

Recently, Rögl & Egger (2012) redescribed Globorotalia salisburgensis Gohrbandt, 1967, originally described from Eocene deposits of the Helvetic nappe system (north Salzburg, Austria). These authors provided SEM images of a G. salisburgensis paratype and a drawing of the holotype that they included in Igorina. Upon close examination these new figures show an asymmetrically biconvex test with a strongly convex umbilical side, angular peripheral margin, equatorial outline that is slightly lobate, strongly curved sutures on the spiral side, and apparently praemuricate and encrusted wall texture. However, the overall wall texture and morphology are very similar to the Paleocene genus Igorina. In view of its uncertain taxonomic affinities, we prefer not to include G. salisburgensis in the P. broedermanni group.

In agreement with Berggren et al. (2006a), Globorotalia mattseensis and G. wartsteinensis erected by Gohrbandt (1967) and Acarinina planodorsalis Fleisher, 1974, are morphotypes that fall within the variability of P. broedermanni.

Phylogenetic relationships. Pearsonites nov. gen. likely evolved from the Acarinina mckannai-soldadoensis plexus in the late Paleocene (Zone P5; Soldan et al., 2011; Fig. 10). We have observed that P. broedermanni evolved from P. lodoensis in the middle part of Zone P5 (late Paleocene) by increasing the number of chambers (6–7) in the final whorl, culminating in the evolution of P. anapetes (8–10 chambers; Fig. 10). In the evolution of the P. broedermanni group, the sutures initially change from slightly curved in P. lodoensis to curved in P. broedermanni. Pearsonites anapetes, however, displays radial and oblique sutures. In addition, the chambers in P. lodoensis are almost equidimensional, while in P. broedermanni the chambers become tangentially elongate (subrectangular) and in P. anapetes the chambers are radially elongated (subtrapezoidal to subquadrate). In agreement with Blow (1979, p. 914) and Berggren et al. (2006a), we consider P. anapetes as the end-member of the Pearsonites broedermanni lineage.

Distinguishing features. Pearsonites nov. gen. is distinguished from Acarinina in having a biconvex to planoconvex test, a globorotaliform coiling mode, a narrower umbilicus, subglobular to subquadrate chambers on the spiral side and triangular chambers on the umbilical side, and less coarse, more uniformly sized muricae. It differs from Igorina in having a lower trochospire tending to planoconvex, a rounded peripheral margin, a larger umbilicus, and a typically muricate wall texture without a crust on the spiral side.

Geographic distribution. Widely distributed in tropicalsubtropical areas of the world (Indo-Pacific realms, Atlantic Ocean, and Caribbean Sea). It has been also reported from the Tethys, Caucasus Mountains, east Africa, and California. Stratigraphic range. Zone P5–top of Zone E9.